Galapagos shark
Encyclopedia
The Galapagos shark is a species
of requiem shark
, family Carcharhinidae, found worldwide. This species favors clear reef environments around oceanic islands, where it is often the most abundant shark species. A large species that grows to 3.7 m (12.1 ft), the Galapagos reef shark has a typical fusiform "reef shark" shape and is very difficult to distinguish from the dusky shark
(C. obscurus) and the grey reef shark (C. amblyrhynchos). An identifying character of this species is its tall first dorsal fin
, which has a slightly rounded tip and originates over the rear tips of the pectoral fins.
Galapagos sharks are active predators often encountered in large groups. They feed mainly on bottom-dwelling bony fishes
and cephalopod
s; larger individuals have a much more varied diet, consuming other sharks, marine iguana
s, sea lion
s, and even garbage. As in other requiem sharks, reproduction is viviparous, with females bearing litters of 4–16 pups every 2–3 years. The juveniles tend to remain in shallow water to avoid predation by the adults. Galapagos sharks are bold and have behaved aggressively towards humans, and are thus regarded as dangerous. The International Union for Conservation of Nature (IUCN) has assessed this species as Near Threatened
, as it has a slow reproductive rate and there is heavy fishing pressure across its range.
and Edmund Heller
in 1905; subsequent authors moved this species to the genus Carcharhinus. The holotype
was a 65 cm (2.1 ft) long fetus
from the Galapagos Islands
, hence the specific epithet galapagensis.
Garrick (1982) placed the Galapagos shark and the dusky shark at the center of the "obscurus group", one of two major groupings within Carcharhinus. The group consisted of the bignose shark
(C. altimus), Caribbean reef shark
(C. perezi), sandbar shark
(C. plumbeus), dusky shark
(C. obscurus), and oceanic whitetip shark
(C. longimanus), all large, triangular-toothed sharks and is defined by the presence of a ridge between the two dorsal fins. Based on allozyme
data, Naylor (1992) reaffirmed the integrity of this group, with the additions of the silky shark
(C. falciformis) and the blue shark
(Prionace glauca). The closest relatives of the Galapagos shark were found to be the dusky, oceanic whitetip, and blue sharks.
The Galapagos shark is found mainly off tropical oceanic islands. In the Atlantic Ocean
, it occurs around Bermuda
, the Virgin Islands
, Madeira
, Cape Verde
, Ascension Island
, Saint Helena
and São Tomé Island
. In the Indian Ocean
, it is known from Walter's Shoal off southern Madagascar
. In the Pacific Ocean
, it occurs around Lord Howe Island
, the Marianas Islands, the Marshall Islands
, the Kermadec Islands
, Tupai
, the Tuamotu Archipelago, the Hawaiian Islands
, the Galapagos Islands
, Cocos Island
, the Revillagigedo Islands
, Clipperton Island
, and Malpelo
. There are a few reports of this species in continental waters off the Iberian Peninsula
, Baja California
, Guatemala
, Colombia
, and eastern Australia
.
Galapagos sharks are generally found over continental and insular shelves near the coast, preferring rugged reef
habitats with clear water and strong converging currents
. They are also known to congregate around rocky islets and seamount
s. This species is capable of crossing the open ocean between islands and has been reported at least 50 km (31.1 mi) from land. Juveniles seldom venture deeper than 25 m (82 ft), while adults have been reported to a depth of 180 m (590.6 ft).
One of the larger species in its genus, the Galapagos shark often reaches 3 m (9.8 ft) long. The maximum reported length is 3.7 m (12.1 ft) and the maximum reported weight is 85.5 kg (188.5 lb). This species has a slender, streamlined body typical of the requiem sharks. The snout is wide and rounded, with indistinct anterior nasal flaps. The eyes are round and of medium size. The mouth usually contains 14 tooth rows (range 13–15) on either side of both jaws, plus one tooth at the symphysis
(where the jaw halves meet). The upper teeth are stout and triangular in shape, while the lower teeth are narrower; both upper and lower teeth have serrated edges.
The first dorsal fin
is tall and moderately falcate (sickle-shaped), with the origin over the pectoral fin rear tips. It is followed by a low midline ridge running to the second dorsal fin. The second dorsal fin originates over the anal fin. The pectoral fins are large with pointed tips. The coloration is brownish gray above and white below, with a faint white stripe on the sides. The edges of the fins are darker but not prominently marked. The Galapagos shark can be distinguished from the dusky shark in having taller first and second dorsal fins and larger teeth, and it can be distinguished from the grey reef shark in having a less robust body and less pointed first dorsal fin tip. However, these characters can be difficult to discern in the field. These similar species also have different numbers of precaudal (before the tail) vertebrae: 58 in the Galapagos shark, 86–97 in the dusky shark, 110–119 in the grey reef shark.
The Galapagos shark is often the most abundant shark in shallow island waters. In their original description of this species, Snodgrass and Heller noted that their schooner
had taken "several hundred" adult Galapagos sharks and that "thousands" more could be seen in the water. At the isolated Saint Peter and Paul Rocks
along the Mid-Atlantic Ridge
, the resident Galapagos sharks have been described as "one of the densest shark populations of the Atlantic Ocean". At some locations they form large aggregations, though these are not true schools
.
During group interactions, Galapagos sharks are dominant to blacktip shark
s (C. limbatus) but deferent to silvertip shark
s (C. albimarginatus) of equal size. When confronted or cornered, the Galapagos shark may perform a threat display
similar to that of the grey reef shark, in which the shark performs an exaggerated, rolling swimming motion while arching its back, lowering its pectoral fins, puffing out its gills, and gaping its jaw. The shark may also swing its head from side to side, so as to keep the perceived threat within its field of vision. A known parasite of the Galapagos shark is the flatworm
Dermophthirius carcharhini, which attaches to the shark's skin. In one account, a bluefin trevally
(Caranax melampygus) was seen rubbing against the rough skin of a Galapagos shark to rid itself of parasites.
The primary food of Galapagos sharks are benthic bony fishes (including eel
s, sea bass
, flatfish
, flathead
s, and triggerfish
) and octopus
es. They also occasionally take surface-dwelling prey such as mackerel
, flyingfish
, and squid
. As the sharks grow larger, they consume increasing numbers of elasmobranchs (rays
and smaller sharks, including of their own species) and crustacean
s, as well as indigestible items such as leaves, coral, rocks, and garbage. At the Galapagos Islands, this species has been observed attacking Galapagos fur seal
s (Arctocephalus galapagoensis) and sea lion
s (Zalophus wollebaeki), and marine iguana
s (Amblyrhynchus cristatus). While collecting fishes at Clipperton Island, Limbaugh (1963) noted that juvenile Galapagos sharks surrounded the boat, with multiple individuals rushing at virtually anything trailing in the water and striking the boat bottom, oars, and marker buoys. The sharks were not slowed by rotenone
(a fish toxin) or shark repellent
, and some followed the boat into water so shallow that their backs were exposed.
s are sustained by a placenta
l connection formed from the depleted yolk sac
. Females bear young once every 2–3 years. Mating takes place from January to March, at which time scars caused by male courtship bites appear on the females. The gestation period
is estimated to be around one year; the spring following impregnation, females move into shallow nursery areas and give birth to 4–16 pups. The size at birth has been reported to be 61–80 cm (2–2.6 ft), though observations of free-swimming juveniles as small as 57 cm (1.9 ft) long in the eastern Pacific suggest that birth size varies geographically. Juvenile sharks remain in shallow water to avoid predation by larger adults. Males mature at 2.1–2.5 m (6.9–8.2 ft) long and 6–8 years old, while females mature at 2.2–2.5 m (7.2–8.2 ft) long and 7–9 years old. Neither sex is thought to reproduce until 10 years of age. The lifespan of this species is at least 24 years.
Inquisitive and persistent, the Galapagos shark is regarded as dangerous to humans and diving unprotected is not advisable in areas where they are abundant. They are known to approach close to swimmers, showing interest in swim fin
s or hands, and are drawn in large numbers by fishing activities. Fitzroy (1839) observed off St. Paul's Rocks that "as soon as a fish was caught, a rush of voracious sharks was made at him, notwithstanding blows of oars and boat hooks, the ravenous monsters could not be deterred from seizing and taking away more than half the fish that were hooked". Limbaugh (1963) reported that at Clipperton Island
"at first, the small sharks circled at a distance, but gradually they approached and became more aggressive...various popular methods for repelling sharks proved unsuccessful." The situation eventually escalated to the point at which the divers had to retreat from the water. Excited Galapagos sharks are not easily deterred; driving one away physically only results in the shark circling back while inciting others to follow, whereas using weapons against them could trigger a feeding frenzy
. As of 2008, the Galapagos shark has been confirmed to have attacked two people: one fatal attack in the Virgin Islands, and a second, non-fatal, attack off Bermuda.
The International Union for Conservation of Nature (IUCN) has assessed the Galapagos shark as Near Threatened
, as its low reproductive rate limits its capacity to withstand population depletion. There is no specific utilization data available, though this species is certainly caught by commercial fisheries
operating across many parts of its range. The meat is said to be of excellent quality. While still common at areas such as Hawaii, the Galapagos shark may have been extirpated from sites around Central America
and its fragmented distribution means other regional populations may also be at risk. The populations at the Kermadec and Galapagos Islands are protected within marine reserve
s.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of requiem shark
Requiem shark
Requiem sharks are a family, Carcharhinidae, of sharks in the order Carcharhiniformes, containing migratory, live-bearing sharks of warm seas such as the tiger shark, the blue shark, the bull shark, and the milk shark.The name may be related to the French word for shark, "requin", itself of...
, family Carcharhinidae, found worldwide. This species favors clear reef environments around oceanic islands, where it is often the most abundant shark species. A large species that grows to 3.7 m (12.1 ft), the Galapagos reef shark has a typical fusiform "reef shark" shape and is very difficult to distinguish from the dusky shark
Dusky shark
The dusky shark is a species of requiem shark, family Carcharhinidae, occurring in tropical and warm-temperate continental seas worldwide. A generalist apex predator, the dusky shark can be found from the coast to the outer continental shelf and adjacent pelagic waters, and has been recorded from...
(C. obscurus) and the grey reef shark (C. amblyrhynchos). An identifying character of this species is its tall first dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
, which has a slightly rounded tip and originates over the rear tips of the pectoral fins.
Galapagos sharks are active predators often encountered in large groups. They feed mainly on bottom-dwelling bony fishes
Osteichthyes
Osteichthyes , also called bony fish, are a taxonomic group of fish that have bony, as opposed to cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species...
and cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s; larger individuals have a much more varied diet, consuming other sharks, marine iguana
Marine iguana
The Marine Iguana is an iguana found only on the Galápagos Islands that has the ability, unique among modern lizards, to live and forage in the sea, making it a marine reptile. The Iguana can dive over 30 ft into the water. It has spread to all the islands in the archipelago, and is...
s, sea lion
Sea Lion
Sea lions are pinnipeds characterized by external ear-flaps, long fore-flippers, the ability to walk on all fours, and short thick hair. Together with the fur seal, they comprise the family Otariidae, or eared seals. There are six extant and one extinct species in five genera...
s, and even garbage. As in other requiem sharks, reproduction is viviparous, with females bearing litters of 4–16 pups every 2–3 years. The juveniles tend to remain in shallow water to avoid predation by the adults. Galapagos sharks are bold and have behaved aggressively towards humans, and are thus regarded as dangerous. The International Union for Conservation of Nature (IUCN) has assessed this species as Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
, as it has a slow reproductive rate and there is heavy fishing pressure across its range.
Taxonomy and phylogeny
The Galapagos shark was originally described as Carcharias galapagensis by Robert Evans SnodgrassRobert Evans Snodgrass
Robert Evans Snodgrass was an American entomologist and artist who made important contributions to the fields of arthropod morphology, anatomy, evolution, and metamorphosis....
and Edmund Heller
Edmund Heller
Edmund Heller was an American zoologist.Heller attended Stanford University in 1896 and finished his study of zoology with a Bachelor of Arts degree in 1901. From 1926 to 1928 he was curator of mammals at the Field Museum of Natural History in Chicago...
in 1905; subsequent authors moved this species to the genus Carcharhinus. The holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
was a 65 cm (2.1 ft) long fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
from the Galapagos Islands
Galápagos Islands
The Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador, of which they are a part.The Galápagos Islands and its surrounding waters form an Ecuadorian province, a national park, and a...
, hence the specific epithet galapagensis.
Garrick (1982) placed the Galapagos shark and the dusky shark at the center of the "obscurus group", one of two major groupings within Carcharhinus. The group consisted of the bignose shark
Bignose shark
The bignose shark is a species of requiem shark, family Carcharhinidae. Distributed worldwide in tropical and subtropical waters, this migratory shark frequents deep waters around the edges of the continental shelf. It is typically found at depths of , though at night it may move towards the...
(C. altimus), Caribbean reef shark
Caribbean reef shark
The Caribbean reef shark is a species of requiem shark, family Carcharhinidae. It is found in the tropical waters of the western Atlantic Ocean from Florida to Brazil, and is the most commonly encountered reef shark in the Caribbean Sea...
(C. perezi), sandbar shark
Sandbar shark
The sandbar shark, Carcharhinus plumbeus, is a species of requiem shark, family Carcharhinidae, native to the Atlantic Ocean and the Indo-Pacific. It is distinguishable by its very high first dorsal fin and inter-dorsal ridge....
(C. plumbeus), dusky shark
Dusky shark
The dusky shark is a species of requiem shark, family Carcharhinidae, occurring in tropical and warm-temperate continental seas worldwide. A generalist apex predator, the dusky shark can be found from the coast to the outer continental shelf and adjacent pelagic waters, and has been recorded from...
(C. obscurus), and oceanic whitetip shark
Oceanic whitetip shark
The oceanic whitetip shark, Carcharhinus longimanus, is a large pelagic shark inhabiting tropical and warm temperate seas. Its stocky body is most notable for its long, white-tipped, rounded fins....
(C. longimanus), all large, triangular-toothed sharks and is defined by the presence of a ridge between the two dorsal fins. Based on allozyme
Allozyme
Variant forms of an enzyme that are coded by different alleles at the same locus are called allozymes. These are opposed to isozymes, which are enzymes that perform the same function, but which are coded by genes located at different loci....
data, Naylor (1992) reaffirmed the integrity of this group, with the additions of the silky shark
Silky shark
The silky shark is a species of requiem shark, family Carcharhinidae, named for the smooth texture of its skin. It is one of the most abundant sharks in the pelagic zone, and can be found around the world in tropical waters. Highly mobile and migratory, this shark is most often found over the edge...
(C. falciformis) and the blue shark
Blue shark
The blue shark is a species of requiem shark, family Carcharhinidae, that inhabits deep waters in the world's temperate and tropical oceans. Preferring cooler waters, blue sharks migrate long distances, for example from New England to South America. Although generally lethargic, they can move very...
(Prionace glauca). The closest relatives of the Galapagos shark were found to be the dusky, oceanic whitetip, and blue sharks.
Distribution and habitat
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, it occurs around Bermuda
Bermuda
Bermuda is a British overseas territory in the North Atlantic Ocean. Located off the east coast of the United States, its nearest landmass is Cape Hatteras, North Carolina, about to the west-northwest. It is about south of Halifax, Nova Scotia, Canada, and northeast of Miami, Florida...
, the Virgin Islands
Virgin Islands
The Virgin Islands are the western island group of the Leeward Islands, which are the northern part of the Lesser Antilles, which form the border between the Caribbean Sea and the Atlantic Ocean...
, Madeira
Madeira
Madeira is a Portuguese archipelago that lies between and , just under 400 km north of Tenerife, Canary Islands, in the north Atlantic Ocean and an outermost region of the European Union...
, Cape Verde
Cape Verde
The Republic of Cape Verde is an island country, spanning an archipelago of 10 islands located in the central Atlantic Ocean, 570 kilometres off the coast of Western Africa...
, Ascension Island
Ascension Island
Ascension Island is an isolated volcanic island in the equatorial waters of the South Atlantic Ocean, around from the coast of Africa and from the coast of South America, which is roughly midway between the horn of South America and Africa...
, Saint Helena
Saint Helena
Saint Helena , named after St Helena of Constantinople, is an island of volcanic origin in the South Atlantic Ocean. It is part of the British overseas territory of Saint Helena, Ascension and Tristan da Cunha which also includes Ascension Island and the islands of Tristan da Cunha...
and São Tomé Island
São Tomé Island
São Tomé Island, at , is the largest island of São Tomé and Príncipe and is home in 2009 to about 157,000 or 96% of the nation's population. This island and smaller nearby islets make up São Tomé Province, which is divided into six districts. The main island is located 2 km north of the...
. In the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
, it is known from Walter's Shoal off southern Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
. In the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
, it occurs around Lord Howe Island
Lord Howe Island
Lord Howe Island is an irregularly crescent-shaped volcanic remnant in the Tasman Sea between Australia and New Zealand, directly east of mainland Port Macquarie, and about from Norfolk Island. The island is about 11 km long and between 2.8 km and 0.6 km wide with an area of...
, the Marianas Islands, the Marshall Islands
Marshall Islands
The Republic of the Marshall Islands , , is a Micronesian nation of atolls and islands in the middle of the Pacific Ocean, just west of the International Date Line and just north of the Equator. As of July 2011 the population was 67,182...
, the Kermadec Islands
Kermadec Islands
The Kermadec Islands are a subtropical island arc in the South Pacific Ocean northeast of New Zealand's North Island, and a similar distance southwest of Tonga...
, Tupai
Tupai
Tupai is a low-lying atoll in Society Islands, French Polynesia. It lies 19 km to the north of Bora Bora and belongs to the Leeward Islands . This small atoll is only 11 km² in area. Its broad coral reef encloses a shallow sandy lagoon. There are almost continuous long wooded motus on...
, the Tuamotu Archipelago, the Hawaiian Islands
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
, the Galapagos Islands
Galápagos Islands
The Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador, of which they are a part.The Galápagos Islands and its surrounding waters form an Ecuadorian province, a national park, and a...
, Cocos Island
Cocos Island
Cocos Island is an uninhabited island located off the shore of Costa Rica . It constitutes the 11th district of Puntarenas Canton of the province of Puntarenas. It is one of the National Parks of Costa Rica...
, the Revillagigedo Islands
Revillagigedo Islands
The Revillagigedo Islands or Revillagigedo Archipelago are a group of four volcanic islands in the Pacific Ocean, known for their unique ecosystem...
, Clipperton Island
Clipperton Island
Clipperton Island is an uninhabited nine-square-kilometre coral atoll in the eastern Pacific Ocean, southwest of Mexico and west of Central America, at...
, and Malpelo
Malpelo Island
Malpelo Island is an island located from Colombia's Pacific coast, and approximately from Panama's coast. It has a land area of . It is uninhabited except for a small military post manned by the Colombian Army, which was established in 1986. Visitors need a written permit from the Colombian...
. There are a few reports of this species in continental waters off the Iberian Peninsula
Iberian Peninsula
The Iberian Peninsula , sometimes called Iberia, is located in the extreme southwest of Europe and includes the modern-day sovereign states of Spain, Portugal and Andorra, as well as the British Overseas Territory of Gibraltar...
, Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...
, Guatemala
Guatemala
Guatemala is a country in Central America bordered by Mexico to the north and west, the Pacific Ocean to the southwest, Belize to the northeast, the Caribbean to the east, and Honduras and El Salvador to the southeast...
, Colombia
Colombia
Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...
, and eastern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
.
Galapagos sharks are generally found over continental and insular shelves near the coast, preferring rugged reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
habitats with clear water and strong converging currents
Ocean current
An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, Coriolis effect, cabbeling, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun...
. They are also known to congregate around rocky islets and seamount
Seamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
s. This species is capable of crossing the open ocean between islands and has been reported at least 50 km (31.1 mi) from land. Juveniles seldom venture deeper than 25 m (82 ft), while adults have been reported to a depth of 180 m (590.6 ft).
Description
Symphysis
A symphysis is a fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint.1.A symphysis is an amphiarthrosis, a slightly movable joint.2.A growing together of parts or structures...
(where the jaw halves meet). The upper teeth are stout and triangular in shape, while the lower teeth are narrower; both upper and lower teeth have serrated edges.
The first dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
is tall and moderately falcate (sickle-shaped), with the origin over the pectoral fin rear tips. It is followed by a low midline ridge running to the second dorsal fin. The second dorsal fin originates over the anal fin. The pectoral fins are large with pointed tips. The coloration is brownish gray above and white below, with a faint white stripe on the sides. The edges of the fins are darker but not prominently marked. The Galapagos shark can be distinguished from the dusky shark in having taller first and second dorsal fins and larger teeth, and it can be distinguished from the grey reef shark in having a less robust body and less pointed first dorsal fin tip. However, these characters can be difficult to discern in the field. These similar species also have different numbers of precaudal (before the tail) vertebrae: 58 in the Galapagos shark, 86–97 in the dusky shark, 110–119 in the grey reef shark.
Biology and ecology
Schooner
A schooner is a type of sailing vessel characterized by the use of fore-and-aft sails on two or more masts with the forward mast being no taller than the rear masts....
had taken "several hundred" adult Galapagos sharks and that "thousands" more could be seen in the water. At the isolated Saint Peter and Paul Rocks
Saint Peter and Paul Rocks
The Saint Peter and Saint Paul Archipelago is a group of 15 small islets and rocks in the central equatorial Atlantic Ocean. It lies in the Intertropical Convergence Zone, a region of severe storms...
along the Mid-Atlantic Ridge
Mid-Atlantic Ridge
The Mid-Atlantic Ridge is a mid-ocean ridge, a divergent tectonic plate boundary located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. It separates the Eurasian Plate and North American Plate in the North Atlantic, and the African Plate from the South...
, the resident Galapagos sharks have been described as "one of the densest shark populations of the Atlantic Ocean". At some locations they form large aggregations, though these are not true schools
Shoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
.
During group interactions, Galapagos sharks are dominant to blacktip shark
Blacktip shark
The blacktip shark is a species of requiem shark, family Carcharhinidae. It is common to coastal tropical and subtropical waters around the world, including brackish habitats. Genetic analyses have revealed substantial variation within this species, with populations from the western Atlantic Ocean...
s (C. limbatus) but deferent to silvertip shark
Silvertip shark
The silvertip shark is a large species of requiem shark, family Carcharhinidae, with a fragmented distribution throughout the tropical Indian and Pacific Oceans. This species is often encountered around offshore islands and coral reefs, and has been known to dive to a depth of 800 m...
s (C. albimarginatus) of equal size. When confronted or cornered, the Galapagos shark may perform a threat display
Shark threat display
Shark threat display, a type of agonistic display, is a behaviour observed in some sharks when they feel threatened or protective. It consists of a contorting of the body into a series of "ritualized" postures coupled with an exaggerated swimming style...
similar to that of the grey reef shark, in which the shark performs an exaggerated, rolling swimming motion while arching its back, lowering its pectoral fins, puffing out its gills, and gaping its jaw. The shark may also swing its head from side to side, so as to keep the perceived threat within its field of vision. A known parasite of the Galapagos shark is the flatworm
Flatworm
The flatworms, known in scientific literature as Platyhelminthes or Plathelminthes are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals...
Dermophthirius carcharhini, which attaches to the shark's skin. In one account, a bluefin trevally
Bluefin trevally
The bluefin trevally, Caranx melampygus , is a species of large, widely distributed marine fish classified in the jack family, Carangidae...
(Caranax melampygus) was seen rubbing against the rough skin of a Galapagos shark to rid itself of parasites.
Feeding
Eel
Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...
s, sea bass
Serranidae
Serranidae is a large family of fishes, belonging to the order Perciformes. The family contains about 450 species of serranids in 64 genera, including the sea basses and the groupers...
, flatfish
Flatfish
The flatfish are an order of ray-finned fish, also called the Heterosomata, sometimes classified as a suborder of Perciformes. In many species, both eyes lie on one side of the head, one or the other migrating through and around the head during development...
, flathead
Flathead (fish)
A flathead is one of a number of small to medium fish species with notably flat heads, distributed in membership across various genera of the family Platycephalidae. Many species are found in the Indo-Pacific, especially most parts of Australia where they are popular sport and table fish...
s, and triggerfish
Triggerfish
Triggerfishes are about 40 species of often brightly colored fishes of the family Balistidae. Often marked by lines and spots, they inhabit tropical and subtropical oceans throughout the world, with the greatest species richness in the Indo-Pacific...
) and octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...
es. They also occasionally take surface-dwelling prey such as mackerel
Mackerel
Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...
, flyingfish
Flyingfish
Exocoetidae, is a family of marine fish in the order Beloniformes of class Actinopterygii. Fish of this family are known as flying fish. There are about 64 species grouped in seven to nine genera.- Etymology :...
, and squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
. As the sharks grow larger, they consume increasing numbers of elasmobranchs (rays
Batoidea
Batoidea is a superorder of cartilaginous fish commonly known as rays and skates, containing more than 500 described species in thirteen families...
and smaller sharks, including of their own species) and crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, as well as indigestible items such as leaves, coral, rocks, and garbage. At the Galapagos Islands, this species has been observed attacking Galapagos fur seal
Galapagos Fur Seal
The Galápagos fur seal breeds on the Galápagos Islands in the eastern Pacific, west of mainland Ecuador.- Description :...
s (Arctocephalus galapagoensis) and sea lion
Galápagos Sea Lion
The Galápagos sea lion , a species of sea lion, exclusively breeds on the Galápagos Islands and – in smaller numbers – on Isla de la Plata . Being fairly social, and one of the most numerous species in the Galápagos archipelago, they are often spotted sun-bathing on sandy shores or rock groups or...
s (Zalophus wollebaeki), and marine iguana
Marine iguana
The Marine Iguana is an iguana found only on the Galápagos Islands that has the ability, unique among modern lizards, to live and forage in the sea, making it a marine reptile. The Iguana can dive over 30 ft into the water. It has spread to all the islands in the archipelago, and is...
s (Amblyrhynchus cristatus). While collecting fishes at Clipperton Island, Limbaugh (1963) noted that juvenile Galapagos sharks surrounded the boat, with multiple individuals rushing at virtually anything trailing in the water and striking the boat bottom, oars, and marker buoys. The sharks were not slowed by rotenone
Rotenone
Rotenone is an odorless chemical that is used as a broad-spectrum insecticide, piscicide, and pesticide. It occurs naturally in the roots and stems of several plants such as the jicama vine plant...
(a fish toxin) or shark repellent
Shark repellent
A shark repellent is any method of driving sharks away from an area, object, person, or animal. Shark repellents are one category of animal repellents.-Overview:Shark repellents have been of interest to human beings for many years, for a number of reasons...
, and some followed the boat into water so shallow that their backs were exposed.
Life history
Like other requiem sharks, the Galapagos shark exhibits a viviparous mode of reproduction, in which the developing embryoEmbryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s are sustained by a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l connection formed from the depleted yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
. Females bear young once every 2–3 years. Mating takes place from January to March, at which time scars caused by male courtship bites appear on the females. The gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
is estimated to be around one year; the spring following impregnation, females move into shallow nursery areas and give birth to 4–16 pups. The size at birth has been reported to be 61–80 cm (2–2.6 ft), though observations of free-swimming juveniles as small as 57 cm (1.9 ft) long in the eastern Pacific suggest that birth size varies geographically. Juvenile sharks remain in shallow water to avoid predation by larger adults. Males mature at 2.1–2.5 m (6.9–8.2 ft) long and 6–8 years old, while females mature at 2.2–2.5 m (7.2–8.2 ft) long and 7–9 years old. Neither sex is thought to reproduce until 10 years of age. The lifespan of this species is at least 24 years.
Human interactions
Swimfin
Swimfins, swim fins, fins or flippers are worn on the foot or leg and made from finlike rubber or plastic, to aid movement through the water in water sports activities such as swimming, bodyboarding, bodysurfing, kneeboarding, riverboarding, and various types of underwater diving.Scuba divers use...
s or hands, and are drawn in large numbers by fishing activities. Fitzroy (1839) observed off St. Paul's Rocks that "as soon as a fish was caught, a rush of voracious sharks was made at him, notwithstanding blows of oars and boat hooks, the ravenous monsters could not be deterred from seizing and taking away more than half the fish that were hooked". Limbaugh (1963) reported that at Clipperton Island
Clipperton Island
Clipperton Island is an uninhabited nine-square-kilometre coral atoll in the eastern Pacific Ocean, southwest of Mexico and west of Central America, at...
"at first, the small sharks circled at a distance, but gradually they approached and became more aggressive...various popular methods for repelling sharks proved unsuccessful." The situation eventually escalated to the point at which the divers had to retreat from the water. Excited Galapagos sharks are not easily deterred; driving one away physically only results in the shark circling back while inciting others to follow, whereas using weapons against them could trigger a feeding frenzy
Feeding frenzy
In ecology, a feeding frenzy is a situation where oversaturation of a supply of food leads to rapid feeding by predatory animals. For example, a large school of fish can cause nearby sharks to enter a feeding frenzy. This can cause the sharks to go wild, biting anything that moves, including each...
. As of 2008, the Galapagos shark has been confirmed to have attacked two people: one fatal attack in the Virgin Islands, and a second, non-fatal, attack off Bermuda.
The International Union for Conservation of Nature (IUCN) has assessed the Galapagos shark as Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
, as its low reproductive rate limits its capacity to withstand population depletion. There is no specific utilization data available, though this species is certainly caught by commercial fisheries
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
operating across many parts of its range. The meat is said to be of excellent quality. While still common at areas such as Hawaii, the Galapagos shark may have been extirpated from sites around Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
and its fragmented distribution means other regional populations may also be at risk. The populations at the Kermadec and Galapagos Islands are protected within marine reserve
Marine reserve
For the United States Marine Corps Reserve see: Marine Forces ReserveA marine reserve is an area of the sea which has legal protection against fishing or development. This is to be distinguished from a marine park, but there is some overlap in usage...
s.